The invention relates to apparatus for testing the form of gear teeth in which a probe or feeler is movable along the tooth flanks of a workpiece and evaluation of the measurements thus obtained is performed using an electronic computer in which the measurements are compared, according to the progress of the relative movement between the tooth flank and the feeler, with reference values to establish differences between the reference values and actual measured values.
In one known gearwheel tester, the gearwheel to be tested is secured to a base circle disc, which rolls on a fixed generating straight edge. A probe or stylus is arranged on a fixed support and has a contact point with the gear at the starting point of the involute tooth profile on the base circle that agrees with the point of contact between base circle disc and generating straight edge. The probe deflects with deviation of the tooth profile from the involute during the rolling of the testing wheel and as a result indicates the difference between tooth profile and theoretical involute. However, such appliances are only suitable for testing gearwheels of limited diameter, perhaps up to one meter or slightly more, since firstly the base circle disc can only be made up to a limited diameter for technical manufacturing and precision reasons, and secondly the weight of the wheel being tested and rolling on the generating straight edge cannot be unlimited. These restrictions also exist with appliances of which the base circle is adjustable with lever transmissions and auxiliary slides.
For the testing of the profiles of larger gearwheels, appliances are also known in which a base circle segment is fixed on a stationary test wheel or gear and the involute profile is then tested with a probe or stylus, the support of which rolls with a generating straight edge on a base circle segment. Such base circle segments, are however costly and can only be used for a quite specific base circle size, are not capable of being easily centred relatively to the axis of the gearwheel to be tested, and moreover the rolling of the appliance is not capable of being easily controlled, because of its size, so that also here the diameters of the gears that can be tested are also restricted in practice.
Another testing apparatus has been proposed in which the rotation of the gear to be tested is established by means of an angle detector and the associated linear movement of the stylus is measured with a straight edge or linear detector. The pulses of the angle detector and of the linear detector are fed to a digital computer, which compares the measured values with the theoretical involutes and records the calculated deviations by a digital or analog procedure. The necessary rotation of the test wheel or gear, however, also in this case sets limitations as regards diameter and weight (Japanese Specification as laid open No. 18 790/1972).